Lumbrical muscle function as revealed by a new and physiological approach

Area of Science:

• Anatomy
• Biomechanics
• Kinesiology

Background:

• The lumbrical muscle's function in finger extension is established, but its role at the metacarpophalangeal joint remains debated.
• Previous attempts to simulate lumbrical action have been limited by the inability to apply force without predetermining movement direction.

Purpose of the Study:

• To accurately simulate the lumbrical muscle's action and investigate its biomechanical role at the metacarpophalangeal joint.
• To understand the interaction between lumbrical muscle forces and the elastic tension of the flexor digitorum profundus tendon.

Main Methods:

• Development of a novel system using a Bowden cable to simulate lumbrical muscle force application.
• Construction of length-tension curves for the flexor digitorum profundus muscle in fresh cadavers.
• Analysis of lumbrical loads in conjunction with profundus elastic tension.

Main Results:

• The lumbrical muscle exerts a small but significant flexor force at the metacarpophalangeal joint.
• This action contributes to radial deviation and potentially rotation of the finger.
• The lumbrical muscle's numerous muscle spindles suggest a role in monitoring grasp dynamics.

Conclusions:

• The lumbrical muscle actively contributes to metacarpophalangeal joint flexion, radial deviation, and rotation.
• Its unique anatomical position and sensory innervation indicate a role in fine motor control and grasp regulation.